Imposed Water Stress Research Articles

Increasing sustainability by intercropping legume crops with sugar beet under imposed water stress

AbstractThe sustainable use of soil and water resources is a goal that should be pursued to attain food security. This investigation was implemented to compare the effects of three legume intercropping systems with sugar beet on (i) enhancing sugar beet yield under imposed water stress conditions, (ii) soil N contents, (iii) land and water use efficiencies, and (iv) farmers' net income. Two field experiments were carried out in the 2018/19 and 2019/20 seasons in the El‐Minia Governorate, Egypt. The treatments included the interaction between three irrigation treatments: required irrigation ((control, 100% ETc, RI) and two levels of imposed water stress (85% ETc (WS1) and 70% ETc (WS2)), and three intercropping systems: faba bean (FIS), chickpea (CIS) and lentil (LIS) intercropped with sugar beet. The results indicate that the application of implementing CIS and with RI attained higher average values of soil N content (SNC = 14.0 mg kg−1) and net income (NI = US$3,974 ha−1) than those obtained by sugar beet alone. Irrigation with WS1 and the implementation of CIS gave a value of SNC (12.3 mg kg−1) close to that obtained under sugar beet alone irrigated with RI. CIS irrigated with WS1 attained higher averaged values of land equivalent ratio (LER = 1.34), area time equivalent ratio (ATER = 1.28), land equivalent coefficient (LEC = 0.38), water equivalent ratio (WER = 1.12), negative value of change in water use (ΔWU < 0) and NI (US$3,602 ha−1) than those obtained under FIS or LIS irrigated with RI. In conclusion, implementing CIS and irrigation with RI can achieve the sustainable use of land and water. However, implementing CIS and irrigation with WS1 can realize soil improvement, conserve irrigation water and attain higher values of LER, ATER, LEC, WER, and NI than those obtained under FIS, LIS and sugar beet alone.

Deadly acceleration in dehydration of Eucalyptus viminalis leaves coincides with high-order vein cavitation.

Xylem cavitation during drought is proposed as a major driver of canopy collapse, but the mechanistic link between hydraulic failure and leaf damage in trees is still uncertain. Here, we used the tree species manna gum (Eucalyptus viminalis) to explore the connection between xylem dysfunction and lethal desiccation in leaves. Cavitation damage to leaf xylem could theoretically trigger lethal desiccation of tissues by severing water supply under scenarios such as runaway xylem cavitation, or the local failure of terminal parts of the leaf vein network. To investigate the role of xylem failure in leaf death, we compared the timing of damage to the photosynthetic machinery (Fv/Fm decline) with changes in plant hydration and xylem cavitation during imposed water stress. The water potential at which Fv/Fm was observed to decline corresponded to the water potential marking a transition from slow to very rapid tissue dehydration. Both events also occurred simultaneously with the initiation of cavitation in leaf high-order veins (HOV, veins from the third order above) and the analytically derived point of leaf runaway hydraulic failure. The close synchrony between xylem dysfunction and the photosynthetic damage strongly points to water supply disruption as the trigger for desiccation of leaves in this hardy evergreen tree. These results indicate that runaway cavitation, possibly triggered by HOV network failure, is the tipping agent determining the vulnerability of E. viminalis leaves to damage during drought and suggest that HOV cavitation and runaway hydraulic failure may play a general role in determining canopy damage in plants.

Chitosan Induces Sorghum Tolerance to Water Deficits by Positively Regulating Photosynthesis and the Production of Primary Metabolites, Osmoregulators, and Antioxidants

Current climate change scenarios require strategies that mitigate the effects of water deficits. Given that chitosan stimulates induced resistance responses, we tested the hypothesis that foliar application of this polysaccharide can have positive effects on the primary metabolite, antioxidant, and osmoregulatory metabolisms of sorghum, mitigating the effects of water deficit on grain yield. Sorghum plants were cultivated under either irrigated or water-deficit conditions and were either treated or untreated with chitosan, and we assessed the following responses: water potential, gas exchange, nutritional status, biosynthesis of primary and osmoregulatory metabolites, the activity of the antioxidant system constituents, and hydrogen peroxide and malondialdehyde contents. An active methodology was used to impose water stress on plants grown in pots with 20 kg of soil, 06 replications per treatment. Sorghum plants subjected to water deficit that were treated with chitosan exhibited higher stomatal conductance and transpiration than the untreated plants. Water restriction reduced the nutrient contents of leaves, but in the irrigated plants, chitosan treatment increased the tissue contents of certain nutrients and leaf concentrations of total proteins and total amino acids. In the plants under water-deficit conditions that were treated with chitosan, an elevated photosynthetic rate contributed to an increase in carbohydrate accumulation and a higher production of panicle and grain dry biomass compared with the untreated plants. The activity of catalase and ascorbate peroxidase also increased in response to chitosan. Overall, chitosan was effective in enhancing the water deficit tolerance of sorghum plants cultivated under water-deficit conditions by 57%. With this work, we generate perspectives for studies focusing on the development of water-deficit-resistant sorghum lineages, by means of chitosan elicitation.

The influence of silica upon quantitative, qualitative, and biochemical traits of tomato under water stress

Water stress is by far the most serious limiting factor to tomato (Solanum lycopersicom) production, particularly in Iran where located in arid and semi-arid regions. Silicon (Si) is considered an effective element to mitigate the adverse effects of water stress by promoting plant growth and production. Therefore, the present study was designed to evaluate the effects of the foliar application of Si (0, 100, and 200 mg L–1) and three water regimes – no stress (100), mild stress (80%), and severe stress (60%) – on the growth parameters, the yield, and the fruit quality as well as antioxidant status of the tomato. The imposed water stress significantly increased the total soluble solids (TSS), the total acidity (TA), and the flavonoids as well as antioxidant defense parameters such as catalase (CAT) and peroxidase (POX), while the growth parameters (plant height and leaf number) and tomato yield were decreased. In contrast, the foliar application of Si (200 mg L–1) remarkably improved the total yield of tomatoes when exposed to water stress by improving the antioxidant enzyme activities and total flavonoid compounds. In addition, the application of Si could significantly improve the growth parameters (plant height and leaf number) and fruit quality (fruit firmness and size). As a result, the foliar application of Si could be suggested as an effective strategy for imparting water stress resistance in the tomato.

Effect of water stress on weed germination, growth characteristics, and seed production: a global meta-analysis

AbstractWeeds compete with crops for soil moisture, along with other resources, which can impact the germination, growth, and seed production of weeds; however, this impact has not been systematically recorded and synthesized across diverse studies. To address this knowledge gap, a global meta-analysis was conducted using 1,196 paired observations from 86 published articles assessing the effect of water stress on weed germination, growth characteristics, and seed production. These studies were conducted and published during 1970 through 2020 across four continents (Asia, Australia, Europe, and North America). Imposed water stress was expressed as solution osmotic potential (ψsolution), soil water potential (ψsoil), or soil moisture as percent field capacity. Meta-analysis revealed that water stress inhibits weed germination, growth, and seed production, and the quantitative response intensified with increasing water stress. A ψsolutiongreater than −0.8 MPa completely inhibits germination of both grass and broadleaf weeds. A ψsolutionfrom −0.09 to −0.32 MPa reduces weed germination by 50% compared with the unstressed condition. Moderate soil water stress, equivalent to 30% to 60% field capacity, inhibits growth characteristics (branches or tillers per plant, leaf area, leaves per plant, plant height, root, and shoot biomass) by 33% and weed seed production by 50%. Severe soil water stress, below 30% field capacity, inhibits weed growth by 51% and seed production by 88%. Although water stress inhibits weed growth, it does not entirely suppress the ability to germinate, grow, and produce seeds, resulting in weed seedbank accumulation. This creates management challenges for producers, because weed seeds can survive in the soil for many years, depending on weed species and environmental conditions. Quantitative information compiled in this meta-analysis can be instrumental to model the weeds’ multidimensional responses to water stress and designing integrated weed management strategies for reducing the weed seedbank.

Growth and physiological responses of young plants of Dendrocalamus asper (Poaceae: Bambusoideae) under water stress / Crescimento e respostas fisiológicas de plantas jovens de Dendrocalamus asper (Poaceae: Bambusoideae) submetidas a estresse hídrico

Understanding how water stress impacts the growth and physiology of young bamboo plants is important to define management strategies and successful field establishment of the species. In this study, young plants of Dendrocalamus asper were evaluated to determine the effects of water availability in the initial phase of growth and the physiological behavior of the species under these conditions. Four water deficit conditions (0%, 25%, 50% and 100% of field capacity) were applied in a completely randomized design. The plants were grown in pots under a tunnel-type greenhouse environment. At 7 and 30 days of imposition of treatments, growth characteristics and gas exchange were evaluated, and at 30 days, Chl a fluorescence, pigment concentration and dry mass were analyzed. Water stress affected the growth and gas exchange of young D. asper plants. Under lower water availability (25%), the plants had a significant reduction in the dry mass of leaves and stems at 30 days and, interestingly, a greater number of shoots was observed. Although photosynthetic efficiency did not differ statistically, D. asper plants have reduced stomatal conductance (gs) and transpiration (E) under higher water restriction (50% and 25%), and higher PN (net photosynthesis) under 50% of the field capacity. The behavior observed in young plants of D. asper shows tolerance to the level and period of imposed water stress. In addition, shoot emission seems to be the main survival strategy when cultivated under 25% of water availability. This study provides an initial analysis of the impact of water deficit on clonal plantlets of Dendrocalamus asper, and further research is needed to identify the physiological and biochemical mechanisms of this species under greater stress period.

Mulching impact of Jatropha curcas L. leaves on soil fertility and yield of wheat under water stress

In present studies we have evaluated mulching impact of Jatropha curcas leaves on soil health and yield of two wheat (Triticum aestivum L.) varieties Wadan-2017 (rainfed) and Pirsabak-2013 (irrigated) under imposed water stress. Mulch of Jatropha leaves was spread on the soil surface at the rate of 0, 1, 3 and 5 Mg ha−1 after seed germination of wheat. Water stress was imposed by skipping irrigations for one month at anthesis stage of wheat maintaining 40% soil field capacity. We found a significant decline in soil microbial biomass carbon (30.27%), total nitrogen (22.28%) and organic matter content (21.73%) due to imposed water stress in non-mulch plots. However, mulch application at 5 Mg ha−1 significantly improved soil organic matter (38.18%), total nitrogen (37.75%), phenolics content (16.95 mg gallic acid equivalents/g) and soil microbial biomass carbon (26.66%) as compared to non-mulch control. Soil health indicators like soil carbonates, bicarbonates, electrical conductivity, chloride ions and total dissolved salts were decreased by 5 Mg ha−1 mulch application. We noted a decline in yield indicators like spike weight (14.74%), grain spike−1 (7.02%), grain length (3.79%), grain width (3.16%), 1000 grains weight (6.10%), Awn length (9.21%), straw weight (23.53%) and total grain yield (5.98%) of wheat due to imposed water stress. Reduction in yield traits of wheat due to water stress was higher in Pirsabak-2013 than Wadan-2017. Jatropha leaves mulch application at 5 Mg ha−1 significantly minimized the loss in yield traits of wheat crop caused by water stress. Jatropha curcas leaves mulch application at 5 Mg ha−1 is recommended for the successful establishment of wheat crop under water deficit conditions.

Intraspecific Variation for Leaf Physiological and Root Morphological Adaptation to Drought Stress in Alfalfa (Medicago sativa L.).

Drought stress reduces crop biomass yield and the profitability of rainfed agricultural systems. Evaluation of populations or accessions adapted to diverse geographical and agro-climatic environments sheds light on beneficial plant responses to enhance and optimize yield in resource-limited environments. This study used the morphological and physiological characteristics of leaves and roots from two different alfalfa subspecies during progressive drought stress imposed on controlled and field conditions. Two different soils (Experiments 1 and 2) imposed water stress at different stress intensities and crop stages in the controlled environment. Algorithm-based image analysis of leaves and root systems revealed key morphological and physiological traits associated with biomass yield under stress. The Medicago sativa subspecies (ssp.) sativa population, PI478573, had smaller leaves and maintained higher chlorophyll content (CC), leaf water potential, and osmotic potential under water stress. In contrast, M. sativa ssp. varia, PI502521, had larger leaves, a robust root system, and more biomass yield. In the field study, an unmanned aerial vehicle survey revealed PI502521 to have a higher normalized difference vegetation index (vegetation cover and plant health characteristics) throughout the cropping season, whereas PI478573 values were low during the hot summer and yielded low biomass in both irrigated and rainfed treatments. RhizoVision Explorer image analysis of excavated roots revealed a smaller diameter and a narrow root angle as target traits to increase alfalfa biomass yield irrespective of water availability. Root architectural traits such as network area, solidity, volume, surface area, and maximum radius exhibited significant variation at the genotype level only under limited water availability. Different drought-adaptive strategies identified across subspecies populations will benefit the plant under varying levels of water limitation and facilitate the development of alfalfa cultivars suitable across a broad range of growing conditions. The alleles from both subspecies will enable the development of drought-tolerant alfalfa with enhanced productivity under limited water availability.

Effect of Water Stress on Physiological and Morphological Leaf Traits: A Comparison among the Three Widely-Spread Invasive Alien Species Ailanthus altissima, Phytolacca americana, and Robinia pseudoacacia.

Invasive alien species (IAS) are a problem, especially in drought-prone environments such as the Mediterranean Basin where the exacerbation of the already severe conditions could constrain the native species acclimatation degree, creating new opportunities for IAS. Climate change may drive IAS expansions, even if different IAS can vary in their acclimatation response. Thus, it is important to obtain a broader insight of how the different IAS face abiotic stress. This research aimed to compare the effect of the imposed water stress on physiological and morphological leaf traits of Ailanthus altissima (AA), Robinia pseudoacacia (RP), and Phytolacca americana (PA), which are widely spread IAS in the Mediterranean Basin. Our results showed a species-dependent effect of the water stress at a physiological and morphological level, as well as an interaction between species and stress duration. Despite a common strategy characterized by low stomatal control of the photosynthesis, AA, PA, and RP differ in their sensitivity to water stress. In particular, even if AA was characterized by a more water-spending strategy, it was more resistant to water stress than PA and RP. In this view, the key factor was its plasticity to increase leaf mass per area (LMA) in response to water stress.

Effect of Potassium Supply and Water Stress on Potato Drought Tolerance and Water Productivity

ABSTRACT Potato (Solanum tuberosum L.) is one of major food crops grown worldwide and in Lebanon. The response of field grown potato to 0, 200, 300 kg of potassium (K) ha−1 was examined under deficit irrigation (imposed water stress). Trials were conducted under Near East-North Africa (NENA) pedo-climatic conditions found in the semiarid central Bekaa of Lebanon. Irrigation water was provided by a drip irrigation system. A mild deficit irrigation, corresponding to 68% of calculated ET0 in 2015 and 85% of it in 2016, was started at the flowering stage and lasted till foliar senescence. Canopy temperature, at maximum development, showed a slight decrease with the increase of potassium levels. During physiological maturity, the midday leaf temperature was significantly lower at the higher K dose, indicating improved leaf water potential. The highest K dose showed a non-significant, higher, chlorophyll content in the leaves, notably in the first year. A significant increase in the weight of one commercial tuber was found in K300 (247.6 g). The commercial yield ranged between 33.05 and 34.78 Mg ha−1 (K300) and 23.31 and 25.53 Mg ha−1 (K0) in 2015 and 2016 respectively. During the 2016 trial, 8 plots out of 16 had an agronomic water yield between 9 and 13 kg.m−3 against 12 out of 16 plots in 2015, competing with the reported values for potato in the region. Optimizing nutrient and water input in the NENA region can contribute to food security with minimal environmental impact.

Impacts of short-term water restriction on Pelibuey sheep: physiological and blood parameters

One of the projected effects of climate change is a reduction in rainfall in certain regions of the world. Hence, the agricultural and livestock sectors will have to cope with increasing incidences of water shortage while still maintaining productivity levels to feed an ever increasing global population. This short communication reports on the effect of a 2-week water stress on Pelibuey sheep in Cuba. Three treatments were compared, viz. supply of water ad libitum, water supplied once every 3 or 6 days. Following exposure to the water stress, the results showed no changes in sheep body weight or rectal temperature. However, respiration frequency was affected with water stress causing a reduction from 23.3 to 13.3 respirations per min in control and water-deprived animals, respectively. Furthermore, there was evidence for hemoconcentration in response to water stress (levels of hemoglobin increased from 9.2 to 13.1 g L-1 and hematocrits from 27.6 to 39.3% in the control group and animals restricted to water once every 6 days. The imposed water stress was also evident in the reduction of lymphocytes (from ±63 to 43%), and in increase of neutrophils (from approximately 38 to 54%) and leukocytes (from 3133 to 4933 per mm3). The results indicated a decline in the levels of antioxidants, i.e., SOD from approximately 13 to 10 U mg-1 protein and CAT activity from 23 to 9 U mg-1 protein. To the best of our knowledge, this is the first report on the response of Pelibuey sheep to short-term water shortage stress under Cuban environmental conditions.

Gas Exchange, Water Use Efficiency, and Biomass Partitioning among Geographic Sources of Acer saccharum Subsp. saccharum and Subsp. nigrum Seedlings in Response to Water Stress.

Responses to water stress were measured for sugar maple (Acer saccharum subsp. saccharum Marshall) sources from Oklahoma (Caddo sugar maple), Missouri, Tennessee, Ontario, and a black maple (Acer saccharum subsp. nigrum F. Michx.) source from Iowa. Seedling sources were selected for differences in temperature and precipitation of their geographic origins. Seedlings were preconditioned through moist (watered daily) or dry (watered every 4–7 days) cycles and then exposed to prolonged water stress. As water stress increased, dry preconditioned 17-week-old sugar maple seedlings from Oklahoma, Missouri, and Tennessee, sources from warmer, and/or drier climates with greater restrained photosynthesis, stomatal conductance, and water use efficiency than those from cooler and moister climates. Under imposed water stress, the Ontario and Iowa sourced seedlings increased their root to shoot ratios and decreased their specific leaf area, mechanisms for drought avoidance. However, no corresponding changes in these values occurred for Oklahoma, Missouri, and Tennessee sources and for the variable of leaf wilting across all sources. Results from this study suggest greater tolerance of water stress in the Oklahoma, Missouri, and Tennessee ecotypes from the western and southern range of sugar maple resulted primarily with water use efficiency (WUE) rather than other water stress coping mechanisms. Findings from this study provide evidence to support selection of sugar maples sources for forestation.

EFFECTS OF Glomus mosseae AND Pseudomonas fluorescens ON ECO-PHYSIOLOGICAL TRAITS AND ANTIOXIDANT PRODUCTION OF MUNG BEAN UNDER DROUGHT CONDITION

Drought is one of the most critical environmental stressors affecting agricultural productivity around the world and it considerably results in yield. Symbiosis interaction between plants and soil micro-organisms are considered to enhance plant tolerance in a/biotic conditions. In this study, the impact of Glomus mosseae, Pseudomonas fluorescens strain 169 and both of them under imposed water stress (flowering and pod filling stages) of mung bean (Vigna radiata (L.) Wilczek) was evaluated in two farm experiments during 2016 and 2017. Eco-physiological parameters have been recorded which showed that drought stress reduced the number of leaves, root colonization and seeds yield of mung bean. Mixed inoculation of G.mosseae and P.fluorescens 169 was more effective in alleviation the harm effects of drought stress. Enzymes assay suggested that co-inoculation of G.mosseae and P.fluorescens 169 was more effective to increase antioxidative defense system like catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR) activities. H2O2 contents were increased by water stress both in cutting irrigation at flowering and pod filling stages. In conclusion, plants inoculated with combination of G.mosseae and P.fluorescens 169 had less oxidative damage over control plants.

Evaluation of blackgram (Vigna mungo) genotypes for drought tolerance under field and in vitro conditions

Blackgram a rainfed crop often experiences soil moisture deficit that reduces productivity to a large extent, could overcome by using a suitable drought resistant variety. Based on this, the present investigation was carried out during 2018 at Department of Genetics and Plant Breeding, Faculty of Agriculture, Annamalai University to study the drought tolerance in twenty-one blackgram genotypes. The selected genotypes (IC-343943, IC-343947, IC-343962, ABG-11013, KU-11680, TBG-104, VBG-10010, VBG-11011, VBG12005, VBG-12062, VBG-13017, ADT-5, RU-16-9, RU-16-13, RU-16-14, KGB-28, T-9, VBN(Bg)-4, VBN(Bg)-6, VBN(Bg)-7, MDU Local) were evaluated in the field condition for drought tolerance by imposing water stress during flowering and pod setting stages (4060 days after sowing) of the crop. The screening was also carried out in vitro by using PEG6000 at three concentrations viz., 0 bar, -3 bars and -6 bars to assess their seedling response under induced osmotic potential. Reduced growth was observed in all blackgram genotypes for all the characters except for the number of days to first flowering. Based on per se performance of genotypes under water-stressed field condition, the genotypes VBG12005, IC-343943 and IC-343947 were recommended as drought-tolerant genotypes for seed yield. In vitro condition, reduction in germination percentage, plumule and radicle length and biomass yield observed under increasing polyethylene glycol (PEG) induced water stress. In vitro screening of blackgram genotypes using PEG 6000 found that the genotypes VBG-11011, RU-16-9 and VBG-13017 expressed tolerance to drought at seed germination level. Thus, seedling stage screening for drought tolerance alone is not reliable as the tolerance mechanism may vary at different growth stages.

Seedlings from marginal and core populations of European beech (Fagus sylvatica L.) respond differently to imposed drought and shade

Key messageLocal adaptation largely segregates between traits affecting light responses and water relations, but population-level differences in stomatal conductance when growth is unconstrained converge among populations under water stress.Warming temperatures and altered precipitation patterns threaten plant populations worldwide. European beech (Fagus sylvatica) is a species that expresses both high phenotypic plasticity and local adaptation among populations. Beech seedlings’ susceptibility to prolonged drought may be dictated by their immediate light environment. We tested whether seedlings of four beech provenances, from contrasting edaphoclimatic environments, expressed differences in trait responses to imposed water stress under sun and shade treatments. Populations from the southern range margin were expected to display greater water-stress tolerance and core populations’ faster growth rates in the absence of abiotic limitations. Both high light and water stress induced differences in trait responses among provenances, but traits that failed to respond to our experimental treatments likewise did not segregate at the provenance level. Hence, those traits responding to light, e.g., increasing leaf flavonol index and leaf mass area, also tended to differ among provenances. Similarly, there was evidence of local adaptation among provenances in traits, like midday leaf water potential, responding to water stress. Exceptionally, there was a three way interaction water- × -light- × -provenance for stomatal conductance which converged among provenances under water stress. Leaf chlorophyll content also varied both with light and water in a provenance-specific manner. We found core provenances’ growth traits to outperform others under favourable conditions, whereas southern and high-elevation populations displayed traits adapted to tolerate high irradiance. Only stomatal conductance produced a complementary interactive response between light- × -water across provenances, whereas other traits responded less to combined water stress and high irradiance than to either treatment alone.

Water stress and temperature effects on germination and early seedling growth of Digitaria eriantha

Fil: Brevedan, Roberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; Argentina. Universidad Nacional del Sur. Departamento de Agronomia; Argentina

Assessing the effects of in vitro imposed water stress on pineapple growth in relation to biochemical stress indicators using polynomial regression analysis

Knowing the mechanisms that operate under water stress in commercial crops, particularly those that can affect productivity, such as phenolic or cell wall metabolism, is becoming increasingly important in a scenario of global climate change. However, our understanding of how to analyse statistically the relationships between these commonly used biochemical markers of water stress and growth in crops like pineapple, needs to be improved. In the present work, we have addressed the question of whether polynomial regression analysis can be used to describe the influence of selected plant metabolites (chlorophylls, carotenoids, phenolics and aldehydes) on shoot biomass, in response to a mannitol-induced water stress in temporary immersion bioreactors (TIBs). Polynomial regression analysis has been applied to investigate plant stress responses in many species but is very seldom used in in vitro screening studies. Here, the relationship between biochemical indicators (x; independent variable) and shoot growth (y; dependent variable) has been characterised, with y modelled as an nth degree polynomial in x. This statistical approach accommodated for the non-linear (curvilinear) relationships between variables, and the results showed that shoot biomass was negatively, and significantly correlated with soluble phenolics, cell wall-linked phenolics and other aldehydes (characterised by “High” R2 values).

Seedling response to water stress in valley oak (Quercus lobata) is shaped by different gene networks across populations.

Drought is a major stress for plants, creating a strong selection pressure for traits that enable plant growth and survival in dry environments. Many drought responses are conserved species-wide responses, while others vary among populations distributed across heterogeneous environments. We tested how six populations of the widely distributed California valley oak (Quercus lobata) sampled from contrasting climates would differ in their response to soil drying relative to well-watered controls in a common environment by measuring ecophysiological traits in 93 individuals and gene expression (RNA-seq) in 42 individuals. Populations did not differ in their adjustment of turgor loss point during soil drying, suggesting a generalized species-wide response. Differential expression analysis identified 689 genes with a common response to treatment across populations and 470 genes with population-specific responses. Weighted gene co-expression network analysis (WGCNA) identified groups of genes with similar expression patterns that may be regulated together (gene modules). Several gene modules responded differently to water stress among populations, suggesting regional differences in gene network regulation. Populations from sites with a high mean annual temperature responded to the imposed water stress with significantly greater changes in gene module expression, indicating that these populations may be locally adapted to respond to drought. We propose that this variation among valley oak populations provides a mechanism for differential tolerance to the increasingly frequent and severe droughts in California.

Water relations and productivity of two lines of pearl millet grown on lysimeter with two different soil types

Crop water productivity is one of the important aspects of water use of crop, most especially where water is a limiting factor. This study was carried out to assess and compare water relations and productivity of two lines of pearl millet grown on lysimeters with two soil types. The study was carried out at the lysimeter unit of the Department of Soil, Crop and Climate Sciences Experimental Farm, Kenilworth, University of the Free State, Bloemfontein. One row of the unit contains a Clovelly soil and the other row, Bainsvlei soil. The two lines of pearl millet used for the study were GCI 17, improved variety and Monyaloti, a local variety. Irrigation treatments were applied such that water was withheld at the beginning of different growth stages of the crop to impose water stress. These treatments were well-watered (WW), vegetative stage stress (VS), reproductive stage stress (RS), and grain-filling stage stress (GS). The treatments were replicated two times per line of pearl millet per soil type. The results show that the lowest leaf water potential was observed in the GS stress plants for both lines of pearl millet on Bainsvlei soil form. The highest stomatal conductance observed on Clovelly soil was around 400 mmol m−2 s−1 while it was around 300 mmol m−2 s-1 on Bainsvlei soil for the two lines of pearl millet. The highest and lowest grain yields for GCI 17 were from Clovelly soil. The highest grain yield for Monyaloti was 10.74 t ha-1from the WW found on Clovelly soil type while the lowest was 3.93 t ha-1 from GS found on Bainsvlei soil type. The mean water productivity for biomass (WPbm) of GCI 17 was 0.036 t ha−1 mm−1for both soil types while Monyaloti had WPbm of 0.037 and 0.035 t ha−1 mm−1 on Bainsvlei and Clovelly respectively. Clovelly soil type proved to exhibit high water productivity for grain yield production of pearl millet.

Changes in Root Anatomy of Peanut (Arachis hypogaea L.) under Different Durations of Early Season Drought

Changes in the anatomical structure of peanut roots due to early season drought will likely affect the water acquiring capacity of the root system. Yet, as important as these changes are likely to be in conferring drought resistance, they have not been thoroughly investigated. The objective of this study was to investigate the effects of different durations of drought on the root anatomy of peanut in response to early season drought. Plants of peanut genotype ICGV 98305 were grown in rhizoboxes with an internal dimension of 50 cm in width, 10 cm in thickness and 120 cm in height. Fourteen days after emergence, water was withheld for periods of 0, 7, 14 or 21 days. After these drought periods, the first and second order roots from 0–20 cm below soil surface were sampled for anatomical observation. The mean xylem vessel diameter of first- order lateral roots was higher than that of second- order lateral roots. Under early season drought stress root anatomy changes were more pronounced in the longer drought period treatments. Twenty-one days after imposing water stress, the drought treatment and irrigated treatment were clearly different in diameter, number and area of xylem vessels of first- and second-order lateral roots. Plants under drought conditions had a smaller diameter and area of xylem vessels than did the plants under irrigated control. The ability of plants to change root anatomy likely improves water uptake and transport and this may be an important mechanism for drought tolerance. The information will be useful for the selection of drought durations for evaluation of root anatomy related to drought resistance and the selection of key traits for drought resistance.